Crumble the tofu into a bowl. Stir the stock powder into the 1/4 cup hot water and add the soy sauce. Stir this through the crumbled tofu and set aside to absorb the flavour.
Remove the noodles from the packet and soak in cold water (for about 10-15 minutes, while you get the rest of the dish together).
Heat the vegetable oil in a large wok. Add the onion, ginger and garlic. Sauté until the onion is cooked.
Add the marinated crumbled tofu and any remaining liquid in the bowl. Cook until any liquid is dissolved, at least 5 minutes.
Add all the vegetables and the beef stock, soy sauce and ketcap manis. Simmer until the vegetables are just tender and the liquid has reduced to about half.
Drain the noodles that you've been soaking in cold water and throw them in the wok. Stir well and cook for 2-3 minutes until the noodles are cooked and hopefully by this stage you shouldn't have too much liquid left in the wok. I recommend serving immediately - if you leave it hot in the wok the noodles will overcook and break up a lot (not that this matters very much!).